The present invention relates to the field of optics, in particular to focusable optical instruments for observation within confined spaces such as internal cavities of a human body. In particular, the invention relates to a medical endoscope. An endoscope is an instrument for the visual examination of the interior of a body cavity or viscus. Endoscopes have become widely utilized in surgery to permit performance of diagnostic and surgical procedures internally without the need for invasive surgical procedures. An endoscope is typically inserted through a small incision portal providing access to the body cavity. A lens at a distal end of the endoscope is positioned to receive light reflected from a site to be observed, and images of the site can be viewed remotely to conduct histological examinations and to perform closed, or endoscopic, surgery. As used herein, the term endoscope refers generically to viewing devices for remotely observing otherwise inaccessible body cavities with minimal trauma and intrusion, including but not limited to arthroscopes, colonoscopes, bronchoscopes, hysteroscopes, cystoscopes, sigmoidoscopes, laparoscopes, sinoscopes, small-joint dental scopes, ureterscopes, etc.
A typical endoscope includes an elongated flexible or rigid outer tube within which a lens system is disposed at a distal end. The image of the object being viewed by the optical system is transmitted through an optical system from the distal end to a proximal end of the tube for viewing by the user or for reception by a camera. Some endoscopes also carry fiber optic cables for illuminating the area of observation with light supplied by an external source.
One endoscope with a typical focusing mechanism is disclosed, e.g., in U.S. Pat. No. 5,575,757 issued in 1996 to Kennedy, et al. As shown in FIGS. 1 and 2, where FIG. 1 is a sectional view of a distal end and FIG. 2 is a sectional view of a proximal end of the endoscope of U.S. Pat. No. 5,575,757, the endoscope, which is designated as a whole by reference numeral 10, includes an elongated insertion section 12 for insertion into a body cavity or narrow body passage to observe an object therein (not shown). Elongated insertion section 12 extends along a longitudinal axis 13 of endoscope 10 from a distal end 14 to a handle 16 at the proximal end 19 of endoscope 10. Handle 16 permits the user to position elongated insertion section 12 of endoscope 10 appropriately and also houses a focus control mechanism 17 for endoscope 10, which is described in detail below. A cable 18 extends from proximal end 19 for connection to a power source and camera control unit (not shown). Images observed at distal end 14 of endoscope 10 are processed by the video processor for viewing on a display unit.
Elongated insertion section 12 includes an outer tube 20 for housing an objective lens assembly 22, an image transmitting device, e.g., an electro-optic module 23, having an electro-optical sensor 24 (e.g. a charge-coupled device (CCD)) for converting optical images of the received light into electrical image signals), and light guiding fiber optic elements 26 for illuminating the area being observed. Outer tube 20 extends from distal end 14 of endoscope 10 to a first end of a main housing 30 at handle 16 where tube 20 is soldered within a counterbore of main housing 30.
Elongated insertion section 12 further includes an inner cylindrical tube 31 and a CCD tube 32, each coaxially disposed within outer tube 20. Inner cylindrical tube 31 extends from the distal end 14 of the outer tube 20 to an enlarged proximal end 31a that receives the distal end of CCD tube 32. Tube 31 is radially spaced from outer tube 20 to provide a cylindrical passage within which fiber optic elements 26 pass to distal end 14. CCD tube 32 is shown having a first cylindrical member 33 extending from a region directly behind lens assembly 22 to a region partially within main housing 30 and a second extension member 34 soldered to first cylindrical member 33 which extends to focus control mechanism 17. The distal end 33a of CCD tube 32 has a pair of enlarged diameter regions 29a, 29b as shown to receive electro-optic module 23 and a crimped end of cable 18, respectively. Electro-optic module 23 is secured into region 29a of CCD tube 32 with epoxy. Cable 18 has a woven ground conductor surrounded by a band 21, which is crimped to prove a snug fit within region 29b. 
Referring to FIG. 2, focus control mechanism 17 allows a user to focus endoscope 10 by adjusting the distance between objective lens assembly 22 and CCD 24, e.g., by xc2x10.1 mm. As mentioned above, objective lens assembly 22 and CCD 24 are rigidly secured to inner tube 31 and CCD tube 32, respectively. The spacing between CCD 24 and lens assembly 22 is varied by moving CCD tube 32 axially along longitudinal axis 13 of endoscope 10. The front face 25 of CCD 24 is moved by focus control mechanism 17 in response to rotation of focus ring 80 by the user.
Main housing 30 has a through hole 46 extending its length to receive CCD tube 32 and to allow cable 18 to pass through endoscope 10. A pair of oblong slots 48, 50 are disposed through opposite sidewalls of an end portion 65 of main housing 30 for respectively receiving a pair of cam screws 76, 78.
A cylindrical actuator 62 is interposed between main housing 30 and CCD tube 32 and is threaded to receive the proximal end of CCD tube 32. A pair of threaded holes 66, 67 orthogonal to axis 13 are disposed through the walls of actuator 62 and are aligned with oblong slots 48, 50 of main housing 30. A lock nut 63 secures actuator 62 to the proximal end of CCD tube 32.
Along an outer surface of main housing 30 is a cylindrical focus sleeve 68 having a pair of diametrically opposed helical grooves 70, 71 each of which is aligned with a corresponding one of threaded holes 66, 67 of actuator 62 and a corresponding one of oblong slots 48, 50. Each one of a pair of cam bearings 74 having through holes 77 engages a corresponding one of helical grooves 70, 71 and contacts actuator 62 along diametrically opposite helical surfaces of slots 70, 71.
To disassemble focus control mechanism 17, rear housing 102 is unscrewed from the rear portion of main housing 30 and with retainer 104 is drawn along cable 18. Focus ring 80 axially separated from focus sleeve 68 by applying a sufficient force proximally along the length of handle 16 sufficient to separate pin 82 from hole 85 focus sleeve 68. With focus ring 80 removed, cam screws 76, 78 are exposed and can be unscrewed from actuator 62 allowing cam bearings 74 to be removed from through holes 77 of focus sleeve 68. With cam bearings 74 removed, focus sleeve 68 can be slid off of the end of main housing 30.
Thus, by rotating focus control mechanism 17, the user shifts the front face 25 of CCD 24 relative to the objective lens assembly 22 due to interaction of the actuator 62 with helical slots 70 and 71.
The endoscope of U.S. Pat. No. 5,575,757 described above is characterized by the following disadvantages. First of all, the distal end 12 of the endoscope, which is insertable into the human body has a complicated construction as it contains the entire objective optical assembly 22 and moving parts of the focusing mechanism, i.e., the image-sensing device 24. In other words, the image-sensing device 24 is an integral part of the endoscope itself This means, that the endoscope of U.S. Pat. No. 5,575,757 is inapplicable as an attachment to an external image sensing device such as a CCD camera connected to a monitor. At the same time, modern clinics are normally equipped with external image sensing devices, which are widely used in practice. Furthermore, the endoscope of U.S. Pat. No. 5,575,757 has a plurality of threaded connections and seals, so that disconnection of the disposable part is a time consuming operation. Disassembling procedure is accompanied by violation of sealing conditions inside the endoscope.
The endoscope of the aforementioned construction is not autoclavable as an integral unit, as it has relatively movable inner parts. It is stated in the aforementioned patent that the insertable portion, i.e., the distal end 12, is disposable. Thus, an expensive part of the entire unit that contains objective optical assembly and the image-sensing device is disposed after the first use.
Attempts have been made to provide autoclavable endoscopes that can be sterilized without disassembling. One such construction is disclosed in U.S. Pat. No. 5,599,278 issued in 1997 to E. Hibbard. This autoclavable endoscope has a housing, an eyepiece, an insertion tube, proximal and distal windows, and seals that seal against the passage of contaminants into the endoscope during autoclaving. The housing, eyepiece, insertion tube, windows and light pipe are comprised of materials, which withstand a temperature of at least about 650xc2x0 C. (1200xc2x0 F.). However, this endoscope does not have a focusing mechanism, which is a significant disadvantage.
One of the most recent inventions in U.S. Pat. No. 6,019,719 issued to D. Schulz in February of 2000 relates to an electronic endoscope with a semiconductor image sensor (CCD chip) for receiving the images received by an objective. The endoscope has an electronic circuit and comprises a shaft with a distal end and a proximal end, and the objective and CCD chip which are arranged at the distal end. The proximal end is held in a housing, which holds the shaft and encloses the glass-fiber optical connection. The component parts of the CCD chip unit arranged behind the objective, namely the crystal filter, IR cutoff filter and CCD chip, are arranged so as to be spaced from one another. This endoscope is autoclavable and has focusing capability performed electronically. However, this endoscope has extremely sophisticated and expensive construction that envisage insertion of the miniature visualizing device together with associated signal processing equipment into the human body.
It is an object of the present invention to provide a focusable endoscope which is autoclavable as an integral unit, has an entirely sealed autoclavable optical assembly, has no internal moving optical components, is provided with an external focus adjustment sealed independently of the optical system, is characterized by an entirely reusable construction as a whole, has an image plane outside of the endoscope enclosure, is inexpensive to manufacture, easy to use, easy to assembly and disassemble, has an optical performance which is not affected in case of damage of the seals, and is compatible with a variety of existing external image-sensing devices.